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Since these are not particles as we usually think of them, they don't_______________________________________________
have a well defined size...it isn't that they occupy some space that
termininates abruptly. Size is a macroscopic concept that seems to
have little precise meaning microscopically.
As pointed out diffraction techniques give information about periodic
spacings, not size. Even something like scanning tunnelling microscopy
does not show atom size, if such a term were really meaningful, rather
it shows the spacial distribution of electron density.
Of course when one thinks that way, real objects don't terminate
abruptly, they all have some sort of roughness with hills and valleys,
but I think that is a different issue than the really microscopic one.
cheers,
joe
On Jul 6, 2005, at 2:14 PM, Ludwik Kowalski wrote:
On Wednesday, Jul 6, 2005, at 14:15 America/New_York, Bernard Cleyet
wrote:
. . . I must be msng. something here, as I thought booth LEED
and old ordinary X-ray diff. would do this. . . .
Is it not true that X-ray crystalography gives as distances between
scattering centers (atoms) and not sizes of atoms? To estimate sizes of
atoms one can assume that (in solids) they "essentially touch each
others."
The size of an atomic nucleus can be operationally defined in terms of
ranges of nuclear forces. Can the size of an atom be operationally
defined in the same way?
Ludwik Kowalski
Let the perfect not be the enemy of the good.
Joseph J. Bellina, Jr. Ph.D.
Professor of Physics
Saint Mary's College
Notre Dame, IN 46556